In a power semiconductor module that is used in a power conversion device and so forth and builds therein power semiconductor elements such as an IGBT, a power field effect transistor and so forth, die bond joining that performs internal connection of electronic components is performed between the power semiconductor chip and a substrate, and the solder is used in this die bond joining.
Recently, a lead-free solder containing no lead component has been used as a substitute for an Sn—Pb based solder because of environmental problems. As the solder to be applied to the power semiconductor module, an Sn—Ag based lead-free solder that is good in solder wettability, mechanical characteristics, resistance of heat transfer and has given satisfactory results in application to products is mostly used, in the currently known lead-free solders of various kinds of compositions (for example, see Patent Literatures 1 to 6)
Here, Patent Literature 1 discloses to connect a first electrode formed on an electronic component with an Ag-containing electrode formed on a circuit substrate, by using Bi-containing multicomponent system lead-free solders such as an Sn—Ag—Bi based one, an Sn—Ag—Cu—Bi based one and so forth.
In addition, Patent Literatures 2 and 3 disclose to join a substrate electrode with an electronic component electrode, by using Cu-containing multicomponent system lead-free solders such as an Sn—Ag—Cu based one, an Sn—Cu, an Sn—Cu—Ni one and so forth.
In addition, Patent Literatures 3 and 4 disclose to join a substrate with an electronic component, by using Ni-containing multicomponent system lead-free solders such as Sn—Ni—Ag and Sn—Ni—Ag—Cu based ones and so forth.
In addition, Patent Literature 5 discloses to join the substrate with the electronic component, by using an Sn—Ag—Ni—Cu-containing multicomponent system lead-free solder.
In addition, Patent Literature 6 discloses Sn—Sb—Co based or Sn—Sb—Fe based, Sn—Ag—Co based, Sn—Ag—Fe based lead-free solders.
In addition, as cited in later-mentioned description relevant to a relation between a solder composition of the present invention and surface tension, in Non-Patent Literature 1, that a solder material becomes small in surface tension at a temperature that is higher than a melting temperature by at least 25° C. and the surface tension does not change so much even at a temperature higher than that is described.